experiments were mailer than those employed by Pungor and Zapp, the contribution of aluminum to total emission a t 671 mp had to be taken into account. The use of lithium-free metal as a blank caused erratic results when determinations a t low lithium levels, which required coiisiderable signal amplification, were attempted. However, the use of the bsse-line method of background correction, as described by Dean (4), gave much more reproducible measurements. I n tfis method, transmittance values are read first a t the emission peak, then a t wavelengths on either side of the penk, and the interpolated value is used as background. On recording instruments, a line is drawn through the nlinimum readings on either side of the peak. The background intensity is determined by the point of intersect of h i s baseline with a vertical line drawn through the transmittance peak (Figure 3). Interfering Elements. Cu, Mn, Cr, Ni, Zn, and T i in concentrations up t o 0.2% in aluminun: do not interfere from the standpoint of emission enhancement or suppression. However, if silicon is present in larger amounts, some atomizer clogging may occur. Filtration OIL a rapid paper is recommended in this case. Mag-
region are not usually found in aluminum. At the recommended slit width of 0.1 mm., resolution of the 671mp lithium line by the DU monochromator of the Spectracord is satisfactory.
1
ACKNOWLEDGMENT
The authors are indebted to C. A. Broyles, Reynolds Metals Co., Malvern, Ark., for his assistance in evaluating the method.
EMISSION INTENSITY
LITERATURE CITED
WAVE
Figure 3. rection
LENGTH
Method of background cor-
nesium suppresses lithium when present in amounts greater than 5%, but in pure metal, the effect is insignificant. Iron may be tolerated up t o 0.5%. Sodium has no measurable effect up t o 5 mg. per 100 ml. of sample. In the wavelength region under consideration, spectral interferences are at a minimum. Interference from the Sr lines a t 666 mp and 680 mp was not investigated, since this element and others having significant emission in this
(1) Brewster, D., Claussen, C., Iron Age 166, No. 18, 88 (1950). (2) Buell. B. E., ANAL. CHEM.34, 635
. (1962): (3) Dean, J. A., “Flame Photometry,” pp. 51-64, McGraw-Hill, New York, 1w,n. (4)bid., pp. 99-100. (5) Zbid., p. 103. (6) Zbid., pp. 155-60. ( 7 ) Dean, J. A., Carnes, W. J., Analyst 87, 743 (1962). (8) Hourigan, H. D., Robinson, I. W., Anal. Chim. Acta 13, 179 (1955). (9) Zbid., 16, 161 (1957). (10) Pungor, E., Zapp, E. Magy. Kern. Folvoirat. 66. 523 (1960): Anal. Abstr. . 8, $791 (1961). I ,
RECEIVED for review Bpril 22, 1063. Accepted July 25, 1963. Presented at 10th Detroit Anachem Conference, Detroit, Mich., Oct. 22, 1962.
Improved Spectrophotometric Method for the Determination of Small Amounts of Chloroform MARIANNA MANTEL, MAGDA MOLCO, and MARIANNA STILLER Israel Atomic Energy Commission, Rehovoth, Israel
b The reddish color obtained on addition of pyridine io a chloroform solution in the presence of sodium hydroxide (Fujiwara reaction) was used for the qualitative ond quantitative determination of chloroform. By measuring the absorbance at 366 mp instead of 525 mp, and working at optimum conditions established in this report, the sensitivity of the test was considerably increased. The method developed has a relative standard deviation of * 5 % and permits the detection of 0.2 p.p.m. crf chloroform. ADDITION of pyridine to an aqueous chloroform solution and heating for some minutes in presence of sodium hydroxide, a reddish color is obtained which depeids on the concentration of chloroform. The mechanism of the reaction :s not known, but the following has been proposed ( 3 ) .
N
0
-,,,OH;
N- C1 I
+ NaCl + H,O N=CH
CHONa
CHCI,
CHC12
Fujiwara (4) used this reaction for detecting chloroform in body fluids and tissues. ’ole ( I ) employed it for quantitative determinations. He compared the color produced by known concentrations of chloroform against standards obtained from acidified alcoholic fuchsin solutions. Though he claimed a limit of detection of 1 p.p.m., he reported that the accuracy of the method was practical only for higher chloroform concentrations. Later authors who determined chloroform in different media did not obtain a sensitivity better than 10 p.p.m. By establishing optimal working conditions, less than 1 p.p.m. of chloroform
in water was determined in the present work. A new absorbance peak, more intense than the maximum a t 528 mp used by previous groups (I-3), was discovered at 366 mp. The 525-mp peak and the red color faded on standing, while the 366-mp peak became more intense. Chloroform may be determined accurately by this method only in the absence of other polyhalogen compounds such as chloral and trichloroacetic acid, which react similarly. Under certain conditions, the interfering effect of these compounds can be allowed for. EXPERIMENTAL
All the chemicals used R-ere of analytical reagent quality. A Beckman DU spectrophotometer was used. Procedure. Pipet 5 ml. of a n aqueous solution containing from 2 VOL 35, NO. 11, OCTOBER 1963
1737
n
L 0 c
e 2
a
02 I
0
5
IO
I 15
I
20
I 25
I
30
35
Time o f h d o t i n g c m,n
Figure time
3. Effect of length of heating X = 366 mp 2 fig. chloroform per ml.
Wovele ngth Imp)
Figure 1 .
Absorbance spectrum of pyridine layer
-
DISCUSSION AND RESULTS
7. pg. chloroform per ml. 1 -cm. light path cells A. 25 minutes after separation 6. 24 hours later
to 40 pg. of chloroform into a 25-m1. glass-stoppered bottle. Add 5 ml. of pyridine and 10 ml. of 40% (w../n7.) sodium hydroxide, close the bottle, and shake. Heat on a water bath a t 70’ C. for 15 minutes, shaking from time to time, cool to room temperature under the tap, transfer to a 40-ml. separatory funnel, shake, allow to stand for a few minutes until the two layers separate completely, and discard the aqueous layer. Transfer the colored pyridine layer into a 10-ml. volumetric flask, and make up to volume with distilled water. Read the absorbance a t X = 366 mp, using 2-em. light path cells in a Beckman DU spectrophotometer, 1 hour after removal from the water bath, and determine the chloroform content of the sample from the standard curve. Rigorously maintain the time and warming conditions the same as those for the preparation of the standard calibration curve.
Calibration Curve. Prepare a standard chloroform stock solution containing 1 nig. of CHC13 per ml. by weighing 1 grain of chloroform in a very small weighing bottle, introducing i t into a 1-liter volumetric flask, and diluting with distilled water. Pipet 1 nil. of the stock solution into a 100-ml. volumetric flask and make up to volume with water. Introduce aliquots of this solut,ion ranging froin 0.2 t o 5 ml. into 25-nil. glass-stoppered bottles, make up to 5 ml. with watcr, and treat as in “Procedure.”
A series of standards ranging from 0.2 to 5 p.p.m. of chloroform was obtained. A straight-line calibration curve was obtained by plotting the absorbance of these solutions 2’s. chloroform concentration. A
idI
/
07
Y)
---. . -.-
02 01 0
30
-
I / I 60
90
120
150
180
210
240
Time
Lmin. I
Figure 2.
Effect of time factor on absorbance peak 2-cm. light path cells X = 366 mp 6. X = 5 3 0 m u
A.
1738
ANALYTICAL CHEMISTRY
24hr
Absorbance Spectra. The absorbance spectrum was examined in the range 330 to 600 mp within 30 minutes after separation of the pyridine layer. In addition to the known maximum a t 530 mp, a more intensive one was found a t 366 mp (Figure 1). The spectrum was redetermined after 24 hours. The maximum a t 366 mfi increased, whereas that a t 530 mp disappeared (Figure 1). Determination of Optimum Conditions. The optimum conditions for the determination of chloroform were found by investigating the following parameters. EFFECTOF TIMEFACTOR ON ABSORBAWE PEAK. The red color of the pyridine solutions faded on standing. Absorbance a t the two maxima of a sample containing 2 p.p.m. of chloroform was measured a t periods ranging from 10 minutes to 24 hours after preparation of the pyridine extract. As shown in Figure 2, the intensity a t X = 530 mp decreased, while that a t X = 366 mp increased. Both processes were complete after about 260 minutes. The respective minimum and maximum values attained remained constant. Figure 3 shows that the 366-mp absorbance obtained after 1 hour (curve A ) was about 80% of the maximum. The other parameters were investigated using only the 366-mp peak and samples containing 50 pg. of CHC13. LENGTHOF HEATINGTIMEOF ALKALINE SOLUTIONS. Heating the reaction mivture for 15 minutes in a 70’ C. water bath gave optimal absorbance values. This optimum heating time was independent of the time delay required for development of the 366-m~ absorbance peak (Figure 3). Prolonging the heating made the determination somewhat less sensitive. SODIUM HYDROXIDE CONCENTRATIOK. Ten milliliters of NaOH a t concentra-
22 20 18
-
-
::L --__
02
0
2 4 6 8 1 0
Figure 4.
-_
7
20
C
1 30 % w l w NaOH
b 40
Effect of N a O H concentration A. 8. C‘.
>
0
One phase Pyridine layer Aqueous layer
1
2
4
5
6
7 8 9 Vol. of pyridine
1
0
(ml. )
Figure 5. Effect of water-pyridine ratio
= 366 mp
2-cm. light path cells
tions from 2 to 40% (w./w.) were used to prepare the samples. The results are presented in Figure 4. At concentrations below 6% there was no phase separation, no red color was observed, and there was no absorbance a t 530 mp. Nevertheless, the solutions absorbed a t 366 mp. With concentrations higher than 670 (w./w.), two phases, a colorless aqueous layer and a red pyridine layer, separated. The absorbance of both layers was measured :tt 366 mp. The absorbance of the pyridine layer increased with increasing NaOH concentration, while that of the aqueous layer decreased. The highest absorbance of the pyridine layer was obtained with 40% NaOH with almost no absorbance by the aqueous layer. Calibration curves obtained using 10, 20, 30, and 40% (w./w.) of sodium
3
X = 3 6 6 rnp 2.5 pg. chloroform per ml.
hvdroxide indicated that sensitivity increased with more concentrated sodium hydroxide. WATER-PYRIDINE RATIO. Samples containing 5O pg. of were prepared in volumes of water varying from 1 to 9 ml. Pyridine was added, to give a total volume of 10 ml. obtained pigure 5) show The that for the conditions described under “Procedure,” a 1 to 1 ratio of water to pyridine gives maximum absorbance. INTERFERENCE OF OTHER POLYHALOGENS. Several polyhalogenated
Table 1.
Reagent Chloroform Carbon tetrachloride Iodoform Trichloroacetic acid Chloral
compounds also give the Fujinara reaction (4). Samples contairling 40 and 400 ~ g . respectively, , of each were a5 described under ((procedure>, for chloroform, The result, are presented in Table I. PRECISIOK. The precision of the method was found by repeated analysis of three standard samples containing 1, 2% and 4 !-@ Per ml. of chloroform, respecti\ely. The standard deviation, calculated for each series, is given in Table 11.
Absorbance of Various Polyhalogens at 366 Mp
per ml. in final solution
pg.
4 4 40 4 40 4
4 Table 11.
Absorbance at 366 mp 1.58 0.026 0.19 0.095
0.88 1.28 1.40
1.o
No red color
obtained
Precision of Method
Precision, rel. std.
CHCla, pg. per ml.
Taken
Remarks
dev., % 2z4.79
Rel. error, %
Found
Mean
Std. dev.
0.9 0.94 0.96
0.97
10.0465
2.006
&0.061
13.06
0.3
3.86
10.208
35.4
1 .0
3.3
1.o 0.99 1.03
2.0
Figure 6.
r/m .l -CHC1,._ Calibration curves
A. h = 5 3 0 rip after 1 hour 8. h = 3 6 6 mp after 1 hour C. X = 366 mp after 24 hours 2-crn. light path ce!lls
2 -08
4.0
3.8
4.08 4.06
3.74 3.60
VOL. 35, NO. 1 1 , OCTOBER 1 9 6 3
1739
Table 111.
Comparison of Methods for Determination of Chloroform Based on Fujiwara Reaction
Temp.
Pyridine added, ml. 2 drops
Author and medium Feigl (3) 2 Fujiwara (P), body fluids 1 Cole ( I ) ,tissue extracts Gettler ( 6 ) ,tissue 5 extracts Daroga ( 2 ) , soil 20 and air Hildebrecht (6), 1 5
cc14
Milton ( 9 ) , urine 5 and blood Hunold ( 7 ) , air 10 Our method (8)
5
of NaOH reac- Heating Concn., tion, time, yo C. mm. X = mp M1. 1 drop 20 100 Few Visual 3 10 100 Just t o Visual boiling 20 100 2 1 Visual
Sensitivity, p.p.m. 20 1 1
10
20
100
1
Visual
10
10
20
100
5
525
30
10
100
3
525
10
5 drops
2.5
20
100
5
525
50
2
0.08 100
5
Filter S 49 Eko I1
10
10
CONCLUSION
It is obvious that the absorliance a t 366 nip is not due to the product that absorbs a t 530 mp, and that the compound that absorbs a t 366 mp is formed from the red compound, since the time necessary for attaining maximum absorbance in the ultraviolet is identical with that necessary for complete fading of the red color (Figure 2).
40
70
15
366
0.2
Using the conditions described under “Procedure,” a considerable increase in sensitivity over previous techniques for chloroform determination was obtained (Table 111). By measuring the absorbance after 4 hours, the sensitivity may be increased by a further 25%. Even by reading the absorbance a t 530 mp, as in previously reported procedures ($4,the sensitivity is increased. Figure 6 shows a comparison of
these three possibilities for determination of absorbance. Table I11 compares the methods used for the determination of chloroform in different media by different authors using the Fujiwara reaction. By changing the working conditions it would probably be possible to develop sensitive methods for other polyhalogen compounds. ACKNOWLEDGMENT
The authors thank Yona Burg for technical help in carrying out the experiments. LITERATURE CITED
(1) Cole, W. H., J. Biol. Chem. 71, 173 (1926). (2) Daroga, R. P., Pollard, A. G., J. Soc. Chem. Ind. 60, 218 (1941). (3) Feigl, “Spot Tests in Organic Analysis, 5th ed., p. 313, Elsevier, London, 1956. (4) Fujiwara, K., SiL. Nut. Ges. Rostock 6 , 33-43 (1916). (5) Gettler, A. S., Blume, H., Arch. Pathol. 11, 554 (1931). (6) Hildebrecht, Ch. D., ANAL. CHEW. 29, 1037 (1957). (7) Hunold, G. A., Schuhlein, R., Z. Anal. Chem. 179, 81 (1961). (8) Mantel, M., Molco, M., Stiller, M., Bull. Res. Council Israel 3, 10A (1961); Proc. of XXIXth Meeting, Israel
E.,
Chemical Society.
(9) Milton, R. R., Duffield, W. D., Lab. Practice 3, 318 (1954).
RECEIVED for review September 28, 1962. Accepted June 13, 1963.
Spectrophotometric Determination of Acetylenic Compounds as Mercuric Acetate Complexes SIDNEY SIGGIA’ and C. R. STAHL Central Research laboratory, General Aniline & Film Corp., Easton, Pa. A method is presented for determining monosubstituted and disubstituted acetylenic compounds via the triple bond on the molecule. The method is based on the formation of the mercuric acetate addition products of the acetylenic compounds and measurement of the ultraviolet absorption of these addition compounds. The method is selective for acetylenic compounds and is sensitive to low ranges of concentration.
T
EXISTING methods for determining acetylenic compounds are of three types: determination of unsaturation via the addition of bromine, hydrogen, or iodine halide (iodine number) (IS); determination of the acetylenic hydrogen in the case of monosubstituted acetylenes (HC-CR) HE
1740
0
ANALYTICAL CHEMISTRY
(1-6, 7-9, 1 3 ) ; and solvation of the acetylenic compound to the corresponding ketal or ketone and determination of the ketone (11, l a ) . The methods based on addition reactions lack specificity. Ethylenic compounds exhibit the same addition reactions and cause high results. Many organic compounds substitute bromine for hydrogen and oxidiaable compounds consume bromine. The same interferences occur to some extent with iodine halide methods. When the composition of the sample permits, bromination is a rapid and easy means for determining acetylenic compounds. Other reducible compounds interfere with hydrogenation methods by consuming hydrogen, and the methods are usually less precise than other methods for determining acetylenic compounds.
The methods for the determination of monosubstituted acetylenes by replacing the acetylenic hydrogen atom with a metal ion have a higher degree of selectivity than the methods involving addition reactions, but interferences still exist. These methods are either acidimetric or argentometric in nature. Thus, acids and bases in samples limit the use of the acidimetric methods, though in some cases the analysis can be accomplished by first neutralizing the sample. Compounds such as halides, mercaptans, cyanides, and others react with silver, limiting the use of the argentometric methods. These methods, of course, do not apply to disubstituted acetylenes ( R C r C R ’ ) since 1 Present address, O h hlathieson Chemical Corp., New Haven, Conn.
